Mercury tube switch



April 18, 1939. -1l H STALEY 2,155,024

MERCURY TUBE SWITCH Original Filed Jan. 29, 193i; `Z Sheets-Sheet l "wm Inventar,

Jose hf H. Sale 7- isr P il Attorneys.

April 1s, 1,939. J, HSTALEY 2,155,024

MERCURY TUBE SWITCH Original Filed. Jan. 29, 1954 3 Sheets-Sheet 2 "Niv III

IIIIIIlIIIIIfI-I Attorneys.

' Int/anim,

H5 Josep/L H. Staley,

/O Il IZ.

April 1s, 1939. JH. SML-EY 2,155,024

MERGURY'TUBE SWITCH Original Filed Jan. 29, 1934 3 Sheets-Sheet 3 Inventor,

Joseph H. Smiley,

Attorneys.

K Patented Apr. 18, 1939 eric Application Sanitary 29, 1934, Serial Noa i8,844 Renewed March 13, 1937 t Claims.

Reference is made to my application Serial No. 667,323 filed April 1933, for which this applica-z tion is substituted andfalso to my Patent No. 1,906,118 issued April 25, 1933.

5 This invention'relates to the art of electric switches and particularly to that type of switch which employs a uid medium to form a connection or bridge between two electrodes Within an envelope. A primary object of the invention 10 is to provide means for quenching the arc which arises upon breaking a circuit through dow of the bridging medium.

A further primary object ci my invention is to provide means for controlling the location of l5 the arc so that it will not pit or otherwise damage switch parts but will always be located over a medium which is substantially non-deteriorating under the influence oi the arc. This control of the position of the arc is highly essential in 2@ order to prevent the arc from adecting exposed metal or other surfaces so as to preventy contaminating of the fluid with the material of the metal or of such surfaces.

An important advantage ci m3.' invention is 25 that it may be embodied in a strueturehaving a metallic envelope, parts ci which serve directly as electrodes whereby the usual dimculty encourstered in employing fragile envelopes is eliminated.

A further important object ci my invention is 3o to provide sealing means in a two part envelope so as to prevent the admittance oi" atmospheric air and also to prevent the escape of the gas which may he used to fill the envelope. This sealing means is particularly important when the in 3g vention is to be incorporated in a metallic en-1 velope. Y

The duid herein referred to as a suitable me-= dium for providing a bridge between electrodes is preferably mercury and many problems arise 4o when mercury is employed in direct contact with a metallic envelope. If the bridge of mercury between two parts of the envelope is separated in breaking a circuit to have the arc occur directly on or over the metallic surface of the 4@ envelope, pitting or deterioration of the envelope would generally occur with the result that the material thereby removed is taken up by the mercury so ^that the mercury will then have a diierent behavior than it has when in a free 'st-ate. In order to effectively breai-r a circuit through flow oi mercury, it is highly important that the mercury be maintained in such a state that there are no impurities introduced which would cause the mer sf to string out and leave conducting paths after the principal dow ot the mercury. l u

I und that if the arc occurring upon the brest:A of the mercury bridge isquickly quenched and is controlled in location so as to occur over an in- 5 sulat/ed or rather refractory surface removed from the wall of the envelope, whether it be metal, glass, or otherwise, a dependable switch may be had, depending of course upon the employment of an adequate sealing means to prevent atmos- 1o' pheric gases from passing within the envelope and preventing, when employed, inner gases in the envelope from escaping.

A further important object of my invention is to provide means for quenching an arc within the A15 envelope which are automatic in voperation and are made effective by the arc' or iiow or current itseli` so that no moving parts'are required.

While my invention is preferably intended to employ a metallic envelope, it may he embodied 2@ in envelopes of glass, Bakelite and the like ala though such envelopes present the objections oi? being fragile and oi requiring electrodes to he passed and sealed through the envelope whereas the metallic envelopeA may be formed to be uti- 'gg lized directly as the electrodes. The foregoing yobjects and advantages as well as many other@ will become apparent to those versed in the artin the following description of the invention which is made in reference to the accompanying draw1 ings, wherein Fig. l is a side elevation of a structure bodying my invention;

2, an end elevation in partial section; Fig. s, a fragmentary top plan view; Fig. a vertical central longitudinal section through'the envelope in an open circuit positi u; Fig. 5a similar section rocked to the closed circuit position;

Fig. 6, a horizontal longitudinal section in the closed circuit position;

Fig. 7, a detail in vertical longitudinal section of a modified form;

Fig. 8, a vertical central longitudinal section ci a still further modied 'form rocked to the 4i closed circuit position;

Fig. 9,' a similar section rocked to the position where the mercury bridge has just broken;

Fig. lil, a similar section rocked to the fluit open circuit position;

liig. li, an end 'elevation in partial section of the modied form shown in Figs. 8-10;

Fig. i2, a detail in central vertical longitudinal section of a further modiecktorm; Y E

Fig. 13, a detail in' central vertical longitudinal section of a still further modified form;

Fig. 14, a central section through a switch tube showing means for gas sealing together a two part metallic envelope;

Fig. 15, a transverse section on the line I5-I5 in Fig. 14;

Fig. 16, a transverse section on the line I6--I6 in Fig. 14;

Fig. 17, a central vertical longitudinal section through a modified form of the invention employing a glass envelope; y

Fig. 18, anend elevation of the form shown in Fig. 17;

Fig. 19, a central verticallongitudinal section through a further modified form of the invention employing a glass envelope;

Fig. 20, a similar view employing a metallic ring about a portion of the glass envelope to aid in controlling the arc; and

Fig. 21, a central longitudinal section showing a still further modified form of structure employing a glass envelope.

Like characters of reference indicate like parts through the several views in the drawings.

Referring first to the preferred form of my invention wherein a metallic envelope is em.- ployed, reference is made to Figs. 1-16 in the accompanying drawings. I form a tubular body I0 made from metal closed across one end by a metallic wall and open at theother. I have, used a wide' variety of metals including iron, and various alloys, one of which is commercially known as "stainless steel. 'I'he essential characteristics of the metal to be employed are that it be non-amalgamating with mercury and preferably not wetted by the mercury. The external diameter of the body I0 adjacent its open end is reduced so as to receive thereover an insulating bushing II. A metallic cap I2 is formed to havean internal bore adapted to receive the bushing iI therewithin so that the cap may be fitted about the bushingin'telescoping relation with the body I0. The bushing II and cap I2 each have a length greater than the length of the reduced 'diameter portion of the body I0. A refrectory member I3, hereinafter referred to as a breaker, has an external cylindrical surface formed to fit snugly within the bushing II between the open end of the body III and the closed end of the cap I2. 'I'his breakerll3 may be made in a number of different forms such as the form I3' in Figs. 1-7, I3 in Figs. 8-11, and

I3 in Figs. 12 and 13.

' the longitudinal axis` of the body and cap and in that end of the breaker toward the closed cap end. The bore then flares outwardly from this cylindrical shape to form the conical bore I5 flaring out to a diameter equal to that of the internal diameter of the body III.

The breaker I3 as shown in Figs. 8-11 is formed to have a short cylindrical bore centrally disposed about the longitudinal axis of the envelope formed by the body II)` and the cap I2 with the intervening bushing II. The bushing I3 is formed to have an annular lip I6 projecting toward the cap I2. On the other side of the breaker I3 there is provided a counter-bore I1 having a diameter substantially equal to that of the internal diameter of the body, I0, the counter-bore I1 forming a right langle shoulder bev tween it andA the `bore of reduced diameter. The

breaker I3" show'n in Figs. 12 and 13 is in effect a circular disk having a central longitudinal bore therethrough.

Regardless of the particular formation of the* breaker, it is compressively carried within the end of the bushing II so as to be separated by the bushing from direct contact with the vcap I2,

this particular combination being shown by my- Patent No. 1,906,118, issued April 25, 1933. The insulating bushing II- is made of substantially non-deteriorating material which may be suf- -fciently resilient to permit its being used between the body Ill and the cap I2 and over the breaker I3 to give a pressed llt. The bushing II may be made of Bakelite, rubber, casein, wood fiber, and synthetic compositions having similar properties. One particular material suitable for this purpose is a vulcanized `liber composed of approximately 93 per cent cellulose and cellulose derivatives, 6 per cent water, and 1 per cent ash.

It is of course desirable to employ a material that will not become affected by exposure to air. The breaker I3 is preferably made out of some material which will withstand the intense heat of an are. A number of refractory materials are available such as soap stone, lava and fused silica mixtures, one of which mixtures hasas its principal ingredients in approximate proportions silica 49.97 per cent; magnesia 44.62 per cent; and iron 3.44 per cent. This mixture is fused at approximately 2000 vF. and is hard but may be broken under heavy impacts. The breaker I3 made of this or some other suitable refractory material is resiliently supported within the bushing II and thereby spaced from the enveloping Wall of the cap I2. A quantity of mercury I8 is carried within the envelope from which air has been exhausted andpreferably replaced by an inert gas, hydrogen gas being classed as inert and indicated for `the purpose on account of its low cost. Other gases, such as nitrogen and helium may be used. The air may be exhausted and replaced by the gas to be employed by any suitable means, one particular formi being shown by my Patent No. 1,895,177, issued Jan. 24, 1933. In the form shown in Figs. 8-10, the bushing II and the cap I2 have suitable lengths so that when the breaker I3 is placed in the bushing II to have its face flush with theend of the bushing, there is a short gap between the counter bored end of the breaker and the open end of the body I0 in which the bushing II is exposed. This gap provides an annular groove between the breaker and the body. When the tube is tilted to the position as indicated in Fig. 8, the mercury will bridge across and through the breaker I3 to interconnect the body I0 and the cap I2, thereby establishing an electrical connection therebetween. The bore through the breaker I3 is made to have a diameter defining a neck of mercury therethrough of a cross-sectional area which will carry without undue heat--v ing the ilow of current for which the switch is rated.

Now when the tube is tilted back toward the horizontal position as indicated in Fig. 9, the mercury I8 will tend to assume the positions indicated wherein the mercury breaks within the bore of the breaker I3 to leave a quantity within the small vchamber which exists between the breaker I3 and the end of the cap I2. T'he major portion of the mercury will lbe on the body side of the breaker. Further tilting o f the tube to some such position as indicated in Fig. 10 will cause the main portion oi' the mercury which is aisance on the body side of the breaker I3 to flow on down into the body I as indicated. A small globule of mercury I9 will be left within the groove between the breaker and the body end. The globule I9 is provided so that there will always be mercury at the end of the body so as to protect that end. Particular attention is directed to the location of the breaker I3 in reference to the end of the cap i2. One important factor of this location is that the small chamber formed therebetween be so shaped and so proportioned that a globule 2i! of mercury will always remain in that chamber when the tube is rocked from the closed to the open circuit positions and furthermore that once the bridge of mercury has been broken as indicated in Fig. 9, further tilting of the tube will not cause any more mercury to spill over from the globule 20 through the breaker to join the mainv mass. This after spilling is to be avoided so that there is no tendency to reestablish the circuit in any, event and particularly through a small stream of the mercury since such reestablishment would cause a flicker in a lamp circuit and moreover would have a tendency to produce heat within the tube by reason of the fact that this smalli stream would be insufficient in cross-sectional area to carry the current with the result arcing would occur at some point, the location of which would be diiicult to control. Not only is it extremely important to properly proportion the small chamber as indicated, but it is'of the utmost importance to bring the' end or the cap I2 suiiicientiy close to the central bore through the breaker t3 as to establish what is considered to be a rebound wall or a baille so that pressures oi mercury vapor and gases, suddenly created by an arc between theA globule 2d and the main mass of the mercury it, within the breaker bore will be prevented from becoming dissipatedin the direction toward the capand will be so controlled as to cause the effective reduction of the pressure to be through the other end of the breaker bore directed toward the larger opening within the body i0. The structure is so designed as to produce ablast or quick iiow ci the gases through the arcing zone into the larger chamber so as to quench the arc.

The smallest distance that the end of the cap may be spaced from the bore through the breaker it is zero and this would be most eiective were it' not for the fact that the interruption of the current would then be not between two masses of mercury but between mercury and the metal wall of the cap exposed across the end of the breaker bore. 1t is possible that this exposed surface could be made of a suitable alloy so as to resist burning or pitting action of the arc. This would be effective for relatively small'ows of current but where higher flows are to be interrupted, it is much more desirable to interrupt the flow between two masses of mercury. Hence it becomes necessary in many cases to space the cap end a slight distance away from the breaker bore. The greater this distance is the less effective is the arc quenching action of the tube as may be readily seen from the fact that were the breaker to be placed out, for example, midway between the cap and body ends, the pressure would be dissipated equally in both directions without producing any particular flow across the central arcing area. It is therefore believed to be necessary to keep the breaker suiciently close to some wall as will cause the resultant flow of gases to be away from that wall through the arcing area and into a iarger chamber.

For the particular type of construction illustrated in Figs. 8-10, I rind-that for a conservative capactiy of amperes, the cylindrical bore through the breaker I3 may be al; inches in diameter and that the distance between the lip I8 and the inside face of the end of the cap I2 is s inches. The lip itself projects 11g inches from the end of the breaker. The internal diameter of the cap between the breaker and the cap end is 35/54 inches. The length of the cylindrical bore in the breaker is e inches; diameter of counterbore s inches; length of counter-bore inches; internal diameter of the bushing II, 1/2 inches; distance between the breaker I3 and the body i0,

1/8 inches; internal diameter of the body EB, in

inches; and internal length of the body iii, 11% inches. 1t is understood that these dimensions are given as one particular proportion and that the invention is not limited thereto. For the switch tube, a safe rated capacity is 15 amperes at 50 breaks per minute within a i0 degree C. temperature rise, at 110 volts.

The purpose of the lip IS extending into the chamber between the breaker and the cap end is to entrap mercury within that chamber so that there will always be retained the globule 2li therein even though the tube may have been turned entirely up on end with the body I0 lowermost before the circuit is made. This lip also serves to 'prevent after spill following the breaking of the bridge of mercury. Further, this lip permits the provision of a chamber adequate to retain suicient mercury for the rated current capacity in contact with the cap and at the same time permitting the end of the cap to be brought relatively close to the end of the breaker `acrcss the bore therein.

By reason of the peculiar construction above set forth, several very desirable qualities are obtained. rIhe tube having a metallic envelope made of metal is non-breakable. Ascal between the body and cap is obtained through the medium of the intervening insulating bushing l l. in addition to the sealing and insulating properties of the bushing ii, there is the additional feature of the cushion aiorded to-the breaker i3 against blows or impacts received by the metallic Wall. The tube being gas iill'ed with some inert gas such as hydrogen prevents any oxidation from occurring a's might be induced by they arc occurring between the two mercury bodies. The particular formation of the breaker I3 is such that it mechanically tends to separate the main mass of mercury I8 to leave the globule 2U in the small chamber in the cap end without after spill. The sharp shoulder at the body end of the cylindrical bore in the breaker I3 cuts up through the body of mercury It relatively to aid the mercury, through its inherently great surface tension and cohesion, to separate and withdraw from the globule 2u into the larger mass in the body. Shouldfor any reason the arc follow the larger body of mercury toward the end of the body III, there is always the globule I9 left to be the last part of the body electrode so that the arc would not occur in direct contact with the end of the body lll. Again it is to be noted that the separation of the mercury into the globule and main body takes place directly within the small cylindrical bore of the breaker i3, Fig. 9, so that the arcis within this comparatively conned space.

The `location of the breaker in the envelopel yand the diameter of the breaker bore are preferably rnade to be such that the cross-sectionai-.- area oi the mercury bridgevis not less than half of the cross-sectional area of the bore a't the instant of breaking of the bridge, the ideal condition being to maintain that cross-sectional area -of the bridge-substantially equal to the cross- `sectional area of the breaker bore at the instant #are is in intimate contact for a major portion thereof; fourth, thetemperature in the arcing zone is rapidly reduced; fifth, the mercury bridge is magnetically pinched to accelerate the breaking of the bridge; and sixth, the mercury bridge just prior to breaking is magnetically lifted to stretch it and accelerate its breaking. These factors and their effect upon quenching the arc arising upon breaking of the mercury bridge are believed to operate as will now be described.

At the moment of arcing, the space therearound becomes highly ionized and there is an added degree of mercury vaporiza'tion. 'I'his vaporization plus the expansion of the vapor and the gas due to the heat of the arc, sets up a pressure about the arc within the cylindrical bore which of course tends to dissipate itself in all directions. Being confined circumferentiallyl withinthe breaker, there are but two directions in/which the pressure may dissipate, one toward the body I0 and the othertoward the end of the cap I2. There being nothing to hinder the expansion of the gas into the body Il, there is a flow accordingly in that direction. This is further emphasized by the gas attempting to travel in the other direction and striking the cap and so as to'cause a rebound in effect therefrom to follow up the flow of gas toward the body and thereby'accelerating that flow so that thenet result is to cause a blast through the cylindrical bore of the breaker Il across the arcing zone into the body III. This blastvery effectively aids in quenching the arc since the highly ionized charges are carried away from the arcing zone to prevent reestablishment of the arc and the path of the arc itself is tended to be distorted and lengthened Y to increase the resistance thereof. The end wall of the cap I2 may be considered to be in effect a baille which prevents the dissipation of the arc induced pressure'from the breaker theretoward and the body I Il may be considered to be a dissipating chamber into which the pressure is dissipated and reduced by reason of its compara-` tively large volume and cooling-effect.

In addition to this gasblast, it is to be noted that the bore in the breaker is of that size where- -by the' arc occurring therein is closely coniiiied or surround to the end that the occurrence of the arc sets p a great degree of turbulence in that confining space such that the contents are greatlyv agitated and mixed all tending to aid in deionization of the space charge. Allo, to be con- Ts/)iiered is the fact that the wall of .the breaker re either by its cylindrical surface or the sharp shoulder at the end, or both, actually intrudes into the arc when it occurs, .which element again aids in deionization of the arcing zone.

' Heat is also rapidLv dissipatedby the movement in the breaker bore vand radiated through Athe metallic walls of the envelope. In addition to the gas blast effect, the intruding surface, the

turbulence, and the heat dissipation, there is the further pinching effect on the bridge of mercury by reason of the metallic wall of the cap I2 concentrically surrounding the cylindrical bore through the breaker I3. As the4 tube is tilted f from the position indicated in Fig. s to that in netic eld concentrated in the surrounding metallic wall of the cap tends'to further reduce thisneck of mercury in the cylindrical bore by reaso of the concentrated magnetic flux.

This pinchingmefl'ect is set up by the fieldv induced by the ilow of current through the mercury bridge itself and is in additionto the severing action caused by the tilting of the tube to cause the mercury to flow over the breaker Il.

The combined effect of the pinching action plus the mechanically cutting in two of the mercury products a snap action ofthe mercury causing a very quick separation so that this action in itself tends-'to keep the arc at a minimum.

Further advantage is taken of the magnetic field concentrated in the concentrically surrounding metallic ring in that as the neck is reduced by tilting the tube, the'neck-is then at one side of the bore, eccentric of its axis, and the field being then eccentric of the neck tends to-pull that-neck backup into the axis ofthe field, thereby tending to stretch that neck to aid in its severance by the "pull of the mercury masses on either end. VAlso the eccentric eld tends to stretch or curve the arc between the separating mercury masses upwardly to the center of tjhe held.

Referring to Figs. 12 and 13, the breaker I3" is reduced to a disk form and the same properties as above indicated are embodied, particularly as to, the turbulence, the gas blast, and the snap action due to the combined effect of the pinching by the magnetic field` and the tilting of the tube to cut the mercury over the breaker. It is to be noted that the breaker- IS; is resiliently carried by the b'ushing II `as before. In Fig. 13, the breaker I3" is shown as being placed directly against the end of the cap I2, the 'cap I2 being in this case shortened sufficiently so as to reducel the chamber between the cap end and the breaker to zero, this'giving the zero chamber as referred to above wherein the gas blast would be the maximum.

vReferring now to Figs. 14, l5 and 16, the same type of construction is shown as appears in Figs. 8-11. In addition thereto there is indicated a particular means of additionally sealing the Joint between the body III and the cap I2. This sealing means comprises a groove 2| circumferentially cut about thebody Il on that surface fitting within the bushing II; fa groove 22 cut circumferentialiy around the outer side of the bushing II at a distance removed from the groove 2i toward the open body end; and mercury or some semi-solid material in both of the grooves phere or fromi within the tube. I nd that 'it is extremely important to effect a Aseal that will remain gas tight otherwise the tube soon becomes `The breaker andere inoperative. Mercury may be placed in the grooves 2l andi2y by submerging the body iti in a bath of mercury sufficiently deep to come up and ill the groove 22, and while submerged to that depth, the cap I2 and bushing Ii are pressed over the body end.

Attention is now directed to the structure as shown in Figs. 1 6 wherein the only diEerence in structure over that shown in Figs. 8 l3 is in the breaker i3. In this form, the breaker i3' as above indicated has the short bore it which corresponds tothe cylindrical bore in the breaker above described and it is within this bore it that it is desired that the arcing if any occurs. i3', permits the same magnetic pinching and lifting effects on the bridge or neck oi mercury by reason of the encircling band of metal of the cap and also provides for the gas blast to aid in quenching the arc. In the forni as shown in Fig. 7, the breaker I3' is carried directlyin contact with the end of the cap l2 to obtain the zero chamber therebetween corresponding to that above referred to.

Dimensions for one workable size of the structure indicated in Figs. 1-6 are as follows. For a tube switch having a rated capacity the same as of the structure rst described, I form the body to have an internal diameter of 3% inch and a length including that of the breaker of llt inches. The small chamber between the breaker and the cap end has a length of 11.; inch and a diameter or" 11g inch. The diameter of the cylindrical bore lil in the breaker is 1% inch. The small chamber has a depth of 1/8 inch below the bore.

ln either ierm of the invention above described, someV suitable mounting means is provided, one particular iorrn being here shown in Figs. l-3 wherein a hase is provided to carry spaced apart clips 2423 and 225, one set of clips being insulated from the other and both being adapted to receive the tube while therebetween. That is, vthe body i@ will be placed between one set of clips such as the clip @il and the cap l2 would be pressed between the other clip 25. The clips @et and 25 are then placed in the electrical circuit to be closed and opened.

While l have above indicated preferred forms oi my invention as employing'metallic envelopes, the invention may well be incorporated in a glass envelope, one particular form being shownin Figs. i7 and le as an example. En this form a glass envelope 2t is formed to have .an electrode 2l sealed. therethrough and projecting into a well One end of the envelope 2b is sealed a s at ill and the other end has an electrode 3@ carried therethrough in sealed relation, here shown as having a body of metal 3i within the tube forming a wall by its face across that end oi the tube. A small chamber is left immediately in front ci this electrode Si by restricting the walls oi the envelope 26 to form a bore 32 from which the walls slope outwardly into the envelope proper. This iorm is, insofar as setting up a gas blast is concerned, the same as that shown in Figs. 1 5. The envelope 2E', by being formed to have the chamber between the bore 32 and the electrode 3l, gives the same elect and the same formation as is found in the structure in Figs. l-S by employment of the breaker i3. ln the glass envelope form, the globule 2d remains in the chamber in contact with the electrode 3l and the main mass of mercury i8 separates therefrom in the bore 32 so as to have the arc occur substantially within the bore S2 thereby setting up the gas blast the same as occurs within the metallic envelope form shown in Figs. 1-6.

ln Fig. 19 is shown a further modiiled form of glass envelope wherein the bore between the main part of the envelope and the chamber immediately adjacent the end electrode is suciently extended as to dene a cylindrical bore of appreciable length.. lin this form, the arc is more positively controlled and located to be within the bore. The turbulent eect is had within that cylindrical vbore by the close confining of the arc, which includes the arc intruding surface.

lin Fig. 20 is shown substantially the same type of structure as that in Fig. 19 with the addition of a metallic band t3 encircling the cylindrical bore 3i of the envelope. This band 33 is added as a means of concentrating the magnetic flux set up about the mercury bridge so as to accelerate by the splnching and the lifting action the severance of the mercury bridge or neck as the tube may be tilted. Of course it is to be appreciated that in the forms of glass envelope shown in Figs. l720, the envelope must be mounted always to have the electrode y 21 hang downwardly so that these particular 'forms may not be mounted in any other axially rotated positions as may m the'case with the metallic tubes above described.

ln Fig. 21 is shown a still further modified iorm of a structure. in which all of the above indicated are controls may be utilized in quenching the arc. ln this form, a'glass envelope 35 is i'orrned to have a main body from which a neck is extended to have abrupt shoulders between it and the body. Electrodes 3l and 38 are sealed through the end or the neck 36 to enter therewithin and mercury 35 is employed within the envelope to bridge across the inner ends of electrodes 3l? and ti@ when the tube is tilted to raise the 'body end. .e breaker il is employed to protect the glass wall and to conne" the art,vcir cumferentially. ln addition, a metallic ring 'All may be employed to encircle the neck as indicated so that the magnetic iield set up by dow of current through the bridge of mercury between the electrodes may aid in severing the mercury by the pinching and lifting enects. The arc will occur between the ends oi the electrodes within the relatively small bore o the neck 36 so that the gas blast will iiow across this arcing position into the body of the envelope.

'lo summarize,v by my invention, whether it be applied to a metallic envelope or to a. glass or other non-conducting envelope, it is primarly my object to provide in a mercury tube switch, that feature or providing an aro conning wall to have at least part or that wall actually intrude or extend into the arc, and further to so confine the` arc that by reuen oi the restricted arcing space, 'a turbulence is produced in that space; that feature of a blast of gas or vapor through the arcing space; that feature of dissipating heat -from the arcing space; that feature of utilizing the ileld induced by the current dow through the switch to reduce the cross-sectional area of the mer cury bridge; and that feature of also utilizing that iield to lift and stretch that bridge to aid in breaking it, all or said features occurring autornaticallyV and substantially simultaneously to the end that the arc, as may arise upon the breaking of the mercury bridge, may be quickly quenched, principally it is believed, by deionization.

While I have herein shown and described my invention in the forms as now best known to me,l it is obrrious that structural variations may be employed without departing from the spirit of the invention and I, therefore, do not desire to bellimited to those precise forms beyond the limitations as maybe imposed by the following claims.

I claim: Y

l. A mercury switch 'comprising a metallic tubular envelope closed at each endand formed by two partially overlapping, magnetizable but electrically separate parts and each part forming an electrode, a quantity of mercury iiowable longitudinally within the envelope, andv means adjacent one of the electrodes restricting the crosssectional area of the column of mercury when bridging vsaid electrodes, the said restricting means being arranged between said one electrode and the overlapping zone of said parts, whereby an intensied magnetic `i'leld is set up adjacent said restricting means promoting movement of the mercury therefrom by current ow in the mercury.

2. A mercury switch comprising a metallic tubular envelope closed at each end and formed by two partially overlapping magnetizable but electrically separate parts and each part forming an electrode, a quantity of mercury flowable longitudinally within the envelope, and means adjacent one of the electrodes restricting the cross-sectional area of the column of mercury when bridging ,said electrodes, the lsaid restricting means being arranged between said one electrode and the overlapping zone of said parts,

whereby an intensiiied magnetic ield is set up adjacent saidrestricting means promoting movement of the mercury therefrom by current flow in the mercury, the electrode part toward which the mercury flows upon breaking said bridge having less diameter than that of the other electrode.

3. A mercury switch comprising a metallic tubular envelope closed at each end and formed by two electrically separate parts, each part forming an electrode, a quantity of mercury within the envelope owably bridging the electrdes, and means restricting the cross-sectional area of the column of mercury bridging the electrodes, the said restricting means being located adjacent one of the electrodes and the other electrode being magnetizable and having a smaller internal di- Ameter than that of the said one electrode, whereby a severing zone in said column is created by said means and an intensified magnetic field is created adjacent said zone tending to move the column therefrom.

4. In a mercury tube switch, a closed-end envelope, a pair of electrodes, a quantity of mercury bridgeable between the electrodes, means for restricting the cross-sectional area of the mercury bridge between said electrodes, and means concentrating a magnetic eld induced by .current ilow through said mercury tending to move the mercury through said restricting means and toward one oi' the electrodes, said moving of the mercury being normally prevented by gravitational pull on the mercury maintaining said bridge through said restricting means when the switch is rocked to a closed circuit position, said one electrode comprising a mass of magnetizable metal, the cross-sectional .area of which exceeds that of the other electrode.

5. A mercury tube switch comprising in combination, a gas lled metallic tubular envelope closed at both ends and formed by two partially overlapping, magnetizable but electrically.

separate parts each forming an electrode, a quantity of mercury in the envelope shiftable to bridge said electrodes, means adjacent one of said electrodes restricting the cross-sectional area of said bridge, the relationship of the diameter of said area and the maximum spacing of said means from said electrode being on the order of not e ceeding approximately 1% to one.

6. A mercury tube switch comprising in combination, a gas filled metallic envelope closed at both ends and formed by twov partially overlapping magnetizable but electrically separate'parts each forming an electrode, a quantity of mercury in the envelope shlftable to bridge said electrodes,means adjacent one of saidv electrodes restricting the cross-sectional area of said bridge, the relationship of the diameter of said area and the maximum spacing of said means from said electrode being on the order of not exceeding approximately 1% to one, said means maintaining said restricted area for a length not exceeding ap\ proximately three-fourths of the diameter thereof.

JOSEPH H. STALEY. 

